In general, the revolution detecting device of this type is widely used in ordinary industrial machines, agricultural machines and automobiles and the like. Particularity, the revolution detecting device is installed between a transmission and a speedometer cable or near a speedometer in the automobiles as shown in FIG. 1, wherein numeral 1 is a transmission, numeral 2 is a middle connection shaft, numeral 3 is a coupling housing the middle connection shaft therein, numeral 4 is a revolution detecting device having a structure as mentioned below, and numeral 5 is a speedometer cable.
The revolution detecting device 4 comprises a connection shaft 6 rotatably supported by a bearing 7, a permanent magnet body 8 fixed to the connection shaft 6 and a pulse generating means 9 such as a reed switch or the like disposed apart from the magnet body 8. In the conventional revolution detecting device 4 as shown in FIG. 1, the magnet body 8 and the pulse generating means 9 are housed in the same enclosure, so that if foreign matters such as water, dirt and the like penetrate from joint parts between the device 4 and the transmission 1 and speedometer cable 5 or from the inside of the speedometer cable 5 into the inside of the device 4, a short circuit is frequently generated by electrolytic corrosion. Further, the pulse generating means 9 is directly attached to the inner wall of the revolution detecting device 4, so that when a reed switch is used as the pulse generating means 9, there is a problem relating to a vibration resistant property.
The connection shaft 6 is connectable to a cylindrical rotation shaft 1a of the transmission 1 on one hand and to a rotational shaft 5a in the speedometer cable 5 on the other hand. However, when a fitting part 1b of the transmission 1 having male screw threads at its outer periphery is screwed to a fitting part 4a of the device 4 having female screw threads at its inner periphery, eccentricity is apt to be caused between the cylindrical rotation shaft 1a and the connection shaft 6 and hence mechanical loss becomes larger. Therefore, the middle connection shaft 2 capable of absorbing the eccentricity and the coupling 3 housing the middle connection shaft 2 therein are arranged between the rotation shaft 1a and the connection shaft 6. As a result, the number of the parts to be used increases unnecessarily, so that the number of production steps and the production cost increase.
Furthermore, the parts fall down in the assembly operation or the time required for the assembly becomes longer. Moreover, even when using the middle connection shaft, the amount of eccentricity is not yet acceptable. Therefore, the difference between the outer diameter of the middle connection shaft and the inner diameter of the rotation shaft is made large in order to enlarge the acceptable degree of eccentricity. In the latter case, however, the eccentricities of both the shafts themselves become larger and hence the transmission of revolution is not performed smoothly.
It is, therefore, an object of the invention to solve the above mentioned drawbacks of the prior art and to provide a device for detecting the number of revolutions of a connection shaft, which has an excellent vibration resistance and can operate without troubles even when harmful substances such as water, dirt and the like penetrate into the inside of the device.
It is another object of the invention to provide a device for detecting the number of revolutions of a connection shaft, which is simple to assemble and has a structure capable of preventing eccentricity between a rotation shaft and a connection shaft.
According to a first aspect of the invention, there is provided a device for detecting the number of revolutions of a connection shaft, comprising a permanent magnet body attached to the connection shaft and a pulse generating means disposed apart from the magnet body, characterized in that the pulse generating means is arranged in a housing isolated from a casing for the connection shaft carrying the magnet body. In preferred embodiment, an insulating resin fills the housing.
According to a second aspect of the invention, the connection shaft is constructed of a first connection shaft having a radially extended protrusion and a second connection shaft having a cylindrical shape capable of receiving the first connection shaft therein and having an axially extending groove capable of engaging with the protrusion, and further provided with a stopper for controlling the depth of the first connection shaft to be inserted in the second connection shaft and a locking member for preventing the slipping out of both the shafts.
According to a third aspect of the invention, an end of the connection shaft is formed of a cylindrical engaging part capable of receiving therein a rotation conducting shaft with a radially extended protrusion and having an axially extended groove capable of engaging with the protrusion, while a convex curved part having a radially extended protrusion is formed on the other end of the connection shaft, and the cylindrical engaging part is supported by a bearing through a spherical member so as to tilt the connection shaft at the supporting portion of the bearing as a fulcrum, thereby absorbing eccentricity between a rotation output shaft and a rotation conducting shaft which are connected to opposite ends of the connection shaft.